High-strength aluminum alloy extruded material and method for manufacturing the same

ABSTRACT

A high-strength aluminum alloy extruded material contains Si: 0.70 to 1.3 mass %; Mg: 0.45 to 1.2 mass %; Cu: 0.15 to less than 0.40 mass %; Mn: 0.10 to 0.40 mass %; Cr: more than 0 to 0.06 mass %; Zr: 0.05 to 0.20 mass %; Ti: 0.005 to 0.15 mass %, Fe: 0.30 mass % or less; V: 0.01 mass % or less; the balance being Al and unavoidable impurities Crystallized products in the alloy have a particle diameter of a is 5 μm or less. Furthermore, an area ratio of a fibrous structure in a cross section parallel to an extruding direction during hot extrusion is 95% or more.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. §119 to Japanese Application No. 2012-222943, filed on Oct. 5, 2012, entitled “HIGH-STRENGTH ALUMINUM ALLOY EXTRUDED MATERIAL AND METHOD FOR MANUFACTURING THE SAME”. The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an extruded material formed of a high-strength aluminum alloy.

2. Description of Related Art

A 6000 series aluminum alloy material has excellent strength and corrosion resistance, and is used in applications such as mechanical components, structural members and the like. In recent years, the application of a 6000 series aluminum alloy material to frames, etc. of transportation machines such as automobiles has been considered to reduce the weight of the frames, etc.

Examples of high-strength aluminum alloy materials suitably used in automobiles, etc. include the aluminum alloy extruded material described in Patent Document 1 listed below and the aluminum alloy forged material described in Patent Document 2 listed below. The aluminum alloy extruded material described in Patent Document 1 is comprised of a fibrous central structure with a recrystallized surface structure on both sides thereof; it was alleged to have excellent impact absorption properties. Further, the aluminum alloy forged material described in Patent Document 2 is intended to have increased strength due to the addition of 0.4% to 1.2% by weight of Cu in addition to Mg and Si.

PATENT DOCUMENTS

-   Patent Document 1: JP-A 2001-355032 -   Patent Document 2: JP-A 06-330264

SUMMARY OF THE INVENTION

A 6000 series aluminum alloy manufactured within conventional elemental ranges and by a conventional manufacturing method generally has low strength as compared to iron-based materials commonly used in frames. Therefore, it has been required to increase the plate thickness and to impart a shape for reinforcement, for example, by forging, which disadvantageously results in low productivity. Therefore, there is a need in the art to produce a high-strength aluminum alloy material having a proof stress of 350 MPa or more by high productivity extrusion.

However, the aluminum alloy extruded material described in Patent Document 1 has a tensile strength of about 300 MPa, which is an insufficient strength for use in place of iron-based materials.

The aluminum alloy described in Patent Document 2 has higher strength than conventional 6000 series aluminum alloys, but is a forged material that involves the following problem when carrying out the extrusion. Specifically, when the aluminum alloy described in Patent Document 2 is extruded at a high speed, defects may occur on its surface in association with the extrusion, such as surface exfoliation, due to friction against the die, etc., which results in a reduction of the surface quality.

Also, the aluminum alloy forged material described in Patent Document 2 has a relatively high Cu content for 6000 series aluminum alloys, and thus has poor corrosion resistance.

Therefore, in one aspect of the present teachings, a high-strength aluminum alloy extruded material is provided that preferably has excellent corrosion resistance, excellent extrusion productivity and/or an excellent surface quality after extrusion.

In another aspect of the present teachings, a high-strength aluminum alloy extruded material contains Si: 0.70 to 1.3 mass %; Mg: 0.45 to 1.2 mass %; Cu: 0.15 to less than 0.40 mass %; Mn: 0.10 to 0.40 mass %; Cr: more than 0 to 0.06 mass %; Zr: 0.05 to 0.20 mass %; Ti: 0.005 to 0.15 mass %, Fe: 0.30 mass % or less; V: 0.01 mass % or less; and the balance being Al and unavoidable impurities. Crystallized products in the alloy have a particle diameter of 5 μm or less. Furthermore, an area ratio of a fibrous structure in a cross section parallel to an extruding direction during hot extrusion is 95% or more.

In another aspect of the present teachings, a method for manufacturing a high-strength aluminum alloy extruded material, includes producing an ingot which includes Si: 0.70 to 1.3 mass %; Mg: 0.45 to 1.2 mass %; Cu: 0.15 to less than 0.40 mass %; Mn: 0.10 to 0.40 mass %; Cr: more than 0 to 0.06 mass %; Zr: 0.05 to 0.20 mass %; Ti: 0.005 to 0.15 mass %, Fe: 0.30 mass % or less; V: 0.01 mass % or less; and the balance being Al and unavoidable impurities; subjecting the ingot to an homogenization treatment that includes holding the ingot at a temperature of not lower than 450° C. and lower than 500° C. for 2 to 30 hours; subjecting the ingot to hot extrusion in a state where the temperature of the ingot at the start of the hot extrusion is held at 480° C. to 540° C. so as to form an extruded material; quenching the extruded material to 150° C. or lower at a cooling rate of 2° C./sec. to 100° C./sec. while the temperature of the extruded material is held at 480° C. or higher; and thereafter, subjecting the extruded material to an aging treatment that includes heating the extruded material at a temperature of 150° C. to 200° C. for 1 to 24 hours.

The above-described high-strength aluminum alloy extruded material contains the above-specified elements in the above-specified amounts. Therefore, the above-described high-strength aluminum alloy extruded material exhibits excellent corrosion resistance and excellent extrusion productivity, and can easily serve as a high-strength extruded material.

Further, for the above-described high-strength aluminum alloy extruded material, the particle diameter of the crystallized products is restricted to 5 μm or less. Therefore, the high-strength aluminum alloy extruded material is not likely to experience surface exfoliation during the extrusion, and thus can easily exhibit an excellent surface quality after the extrusion.

Furthermore, in the above-described high-strength aluminum alloy extruded material, the area ratio of the fibrous structure in the cross section parallel to the extruding direction during the hot extrusion is 95% or more. Therefore, the high-strength aluminum alloy extruded material can exhibit a proof stress of 350 MPa or more.

Specifically, the above-described high-strength aluminum alloy extruded material can be made as a high-strength extruded material that exhibits excellent corrosion resistance, excellent extrusion productivity and excellent surface quality after extrusion. Furthermore, it can achieve a proof stress of 350 MPa or more due to the synergistic effects of the above specified elements and the metallographic structure constituted in the above manner.

In addition, in a method for manufacturing the above-described high-strength aluminum alloy extruded material, the above-described high-strength aluminum alloy extruded material is manufactured by employing the above-specified processing temperatures, processing times and processing procedures. Consequently, the above high-strength aluminum alloy extruded material can be easily obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a photograph of a metallographic structure of Sample No. 1 having a high area ratio of a fibrous structure in Example 1.

FIG. 2 shows a photograph of the metallographic structure of Sample No. 10 having a low area ratio of a fibrous structure in Example 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The above-described high-strength aluminum alloy extruded material includes 0.70% or more and 1.3% or less of Si and 0.45% or more and 1.2% or less of Mg. When Si and Mg coexist in an alloy, they cause precipitation of Mg₂Si particles during an aging treatment (also known as precipitation hardening or age hardening). Such enhancement of the precipitation increases the (yield) strength of the extrusion material. Further, excess Si that does not precipitate in Mg₂Si particles, for example, makes the Mg₂Si particles fine, and contributes to the improvement of the strength of the above-described extruded material.

If the Si content is less than 0.7%, the amount of precipitated Mg₂Si particles will be relatively low, thereby resulting in a relatively low strength of the resulting extruded material. Therefore, the Si content is preferably 0.7% or more, more preferably 0.85% or more. On the other hand, if the Si content exceeds 1.3%, defects such as exfoliation tend to occur on the surface of the extruded material during extrusion, which may tend to reduce the surface quality of the resulting extruded material. Therefore, the Si content is preferably 1.3% or less, more preferably 1.2% or less.

If the Mg content is less than 0.45%, the amount of precipitated Mg₂Si particles will be relatively low, thereby resulting in a relatively low strength of the resulting extruded material. Therefore, the Mg content is preferably 0.45% or more, more preferably 0.6% or more. On the other hand, if the Mg content exceeds 1.2%, the extrusion productivity deteriorates. For example, the extrusion pressure during extrusion will be increased. Consequently, the surface quality of the resulting extruded material and the productivity of the extruded material are prone to be reduced. Therefore, the Mg content is preferably 1.2% or less, more preferably 0.9% or less.

The Cu content is not less than 0.15% and less than 0.40%. Cu is dissolved in a solid state in an alloy, resulting in enhancement of solid solution. Such enhancement increases the strength of the extruded material. If the Cu content is less than 0.15%, the strength of the resulting extruded material is reduced because the Cu content is insufficient. Therefore, the Cu content is preferably 0.15% or more, more preferably 0.20% or more. On the other hand, if the Cu content is 0.40% or more, the extrusion productivity deteriorates, so that the surface quality and the productivity of the resulting extruded material are prone to be reduced. Furthermore, in this case, the corrosion resistance tends to deteriorate. Therefore, the Cu content is preferably less than 0.40%, more preferably 0.38% or less.

The Mn content is 0.10% or more and 0.40% or less, the Cr content is 0.06% or less (but greater than 0%), and the Zr content is 0.05% or more and 0.20% or less.

Mn, Cr and Zr form Al—Mn based, Al—Mn—Si based, Al—Cr based and Al—Zr based fine intermetallic compounds in combination with Al. The intermetallic compounds, when precipitated in an alloy, suppress recrystallization and thereby increase the ratio or percentage of the fibrous structure in the extruded material. Therefore, if the contents of these three elements are too low, the ratio or percentage of the fibrous structure in the resulting extruded material becomes lower and the strength of the extruded material may be reduced. On the other hand, if the Mn, Cr and Zr contents are too high, the intermetallic compounds become coarse and thereby cause defects such as exfoliation on the surface of the extruded material during the extrusion; consequently, the surface quality of the resulting extruded material is prone to be reduced.

Each of Mn, Cr and Zr suppresses recrystallization independently, and their effects on the suppression of the recrystallization can be further increased by adding these three elements in combination. Therefore, by adjusting (setting) respective the Mn, Cr and Zr contents within the above-specified ranges, the precipitation of coarse intermetallic compounds can be suppressed while increasing the ratio or percentage of the fibrous structure in the extruded material.

The Ti content is 0.005% or more and 0.15% or less. Ti makes the ingot structure fine and increases the ratio or percentage of the fibrous structure in the extruded material. If the Ti content is less than 0.005%, the ingot structure will not be sufficiently fine, such that the ratio or percentage of the fibrous structure will be too low. This tends to reduce the strength and surface quality of the resulting extruded material. On the other hand, if the Ti content exceeds 0.15%, Al—Ti based coarse crystallized products are likely to form with Al. Therefore, defects such as exfoliation tend to occur on the surface of the extruded material during the extrusion, which tends to reduce the surface quality of the resulting extruded material.

The contents of Fe and V are restricted to be 0.30% or less and 0.01% or less, respectively. If the contents of Fe and V are too high, coarse crystallized products are prone to be formed. Therefore, defects such as exfoliation tend to occur on the surface of the extruded material during the extrusion, which tends to reduce the surface quality of the resulting extruded material. Such a reduction in surface quality can be avoided by restricting the contents of Fe and V to 0.30% or less and 0.01% or less, respectively. On the other hand, there are no lower limits of the Fe and V contents. However, to significantly reduce the Fe and V contents, a high-purity aluminum metal must be used, which increases costs without substantial additional benefits. Therefore, in order to avoid excessive material cost increases, the Fe content may be, e.g., 0.05% or more.

The above-described high-strength aluminum alloy extruded material may contain 0.20% or less of Zn. Zn is an impurity mixed, for example, when a recycled material is used, but does not adversely affect the performance of the extruded material when the content thereof is 0.20% or less. On the other hand, if the Zn content exceeds 0.20%, the corrosion resistance of the resulting extruded material may be reduced in some cases.

Further, for the above-described high-strength aluminum alloy extruded material, the particle diameter of crystallized products is restricted to 5 μm or less. During the extrusion, it is highly likely that exfoliation will begin at the crystallized products present in the metallographic structure of the extruded material. However, by restricting the particle diameter of crystallized products to 5 μm or less, defects generated during the extrusion can be suppressed, which improves the surface quality of the extruded material.

The particle diameter of the crystallized products can be measured, for example, by the following method. First, the extruded material is cut to expose its cross section, and the cross section is polished to obtain a smooth surface. Thereafter, the smooth surface is observed with an optical microscope, and the crystallized products in the resulting microscopic image are approximated with an ellipse. The length of the ellipse in the long axis direction is utilized as the particle diameter.

The surface quality of the above-described high-strength aluminum alloy extruded material can be further improved by reducing the content of the crystallized products. For example, the content of the crystallized products is preferably 1% or less. The content of the crystallized products can be determined by obtaining a microscopic image in a manner similar to the above-described particle diameter measuring method, and thereafter, calculating the area ratio of the crystallized products in the microscopic image by means of image processing. This area ratio is utilized as the content of the crystallized products.

In the above-described high-strength aluminum alloy extruded material, the area ratio of the fibrous structure in the cross section parallel to the extruding direction during hot extrusion is preferably 95% or more. The fibrous structure included in the metallographic structure of the extruded material improves the mechanical properties such as tensile strength and proof stress in the extruding direction. Therefore, a high-strength extruded material can be achieved by adjusting the area ratio of the fibrous structure to be 95% or more. The metallographic structure of the extruded material can be confirmed, for example, by performing electrolytic polishing on the cross section of the extruded material, carrying out electrolytic etching for 1 minute at 20° C. and 20 V using a Barker liquid, and then observing the etched cross section using a polarization microscope. Further, the method for calculating the area ratio of the fibrous structure will be explained in further detail in Examples.

As the above-described cross section parallel to the extruding direction during hot extrusion, the cross section that represents the ratio of the fibrous structure present in the metallographic structure can be arbitrarily selected from various cross sections parallel to the extruding direction. Specifically, the cross section parallel to the extruding direction during hot extrusion can be appropriately selected depending on the shape of the extruded material. For example, when the extruded material has a round-bar shape, a cross section passing through the central axis can be selected. When the extruded material has a square-bar shape, a cross section passing through the central axis and vertical to either one of the width and thickness directions can be selected. Further, when the extruded material, for example, is molded into an approximately L-shape as viewed from the extruding direction so as to have a shape with a plate-like portion, a cross section parallel to the thickness (depth) direction of the plate-like portion can be selected. However, the above-described methods for selecting the cross section are merely representative examples, and the cross-section selecting method is not limited thereto.

As was described above, the above-described high-strength aluminum alloy extruded material having the above-specified chemical components (elements) and the above-specified metallographic structure has higher strength than 6000 series aluminum alloy materials produced within conventional elemental ranges and by conventional manufacturing processes and also has excellent corrosion resistance and surface quality. Therefore, the above-described high-strength aluminum alloy extruded material can be suitably and advantageously used as a structural member for vehicles, e.g., as a frame.

Specifically, the above-described high-strength aluminum alloy extruded material can exhibit advantageous properties even in harsh environments, such as vibration and corrosion, and can be suitably used, for example, in a side frame and a door sash of an automobile. Additionally, the high-strength aluminum alloy extruded material exhibiting a proof stress of 350 MPa or more, is suitable for use in a structural member for a vehicle.

Next, a representative method for manufacturing the above-described high-strength aluminum alloy extruded material will be explained. In such a method, an aluminum alloy ingot having the above-specified chemical components (elemental composition) is first produced. During the production of this ingot, the cooling rate during a period of time from tapping to the completion of solidification is preferably controlled to be 0.2° C./sec. or higher. The particle diameter of the crystallized products formed in the ingot can be easily reduced by controlling the cooling rate during casting as described above.

Next, the ingot is subjected to a homogenization treatment that involves holding the ingot at a temperature of not lower than 450° C. and lower than 500° C. for 2 to 30 hours. If the temperature during the homogenization treatment is lower than 450° C., the homogenization of the ingot segregation layer in the metallographic structure of the ingot will be insufficient. As a result, coarsening of crystal grains, formation of an uneven crystal structure, etc. are likely to occur, which may cause a deterioration of the surface quality of the extruded material as the final product. On the other hand, if the temperature during homogenization exceeds 500° C., the AlZr based precipitated product will be transformed, resulting in a reduction of the recrystallization suppressing effect. In this case, the ratio (percentage) of the fibrous structure in the resulting extruded material may be decreased. Thus, the (holding) temperature during the above-described homogenization treatment is preferably not lower than 450° C. and lower than 500° C.

Further, the holding time in the above-described homogenization treatment is preferably 2 hours or longer. If the above holding time is less than 2 hours, the surface quality of the extruded material as the final product is prone to be reduced in a manner similar to as described above due to insufficient homogenization of the ingot segregated layer in the ingot structure. On the other hand, if the holding time in the homogenization treatment exceeds 30 hours, the homogenization of the ingot segregated layer will have been sufficiently achieved and no additional effects can be expected. Thus, the holding time in the homogenization treatment is preferably 2 hours or more and 30 hours or less.

After the homogenization treatment, the ingot is hot extruded in a state where the temperature of the ingot is held at 480° C. to 540° C., thereby resulting in an extruded material. If the temperature of the ingot before extrusion is lower than 480° C., the strength of the resulting extruded material is likely to be reduced due to insufficient dissolution of the added elements. On the other hand, when the temperature of the ingot before extrusion exceeds 540° C., working heat generation during the extruding may locally cause eutectic melting. Therefore, the surface quality of the resulting extruded material may be reduced.

Further, the above-described hot extrusion is preferably carried out within 5 hours from the time when the temperature of the ingot has reached the range of from 480° C. to 540° C. If the hot extrusion is not carried out within 5 hours, the AlZr based precipitated products may be transformed, resulting in a reduction of the recrystallization suppressing effect.

The extruded material obtained by the above-described hot extrusion is quenched to 150° C. or lower at a cooling rate of 2° C./sec. to 100° C./sec. while the temperature is 480° C. or higher. (Hereinafter the “quenching of the extruded material” is referred to as the “quenching treatment” in some cases.) If the temperature of the above-described extruded material before quenching is lower than 480° C., the quench hardening will be insufficient and the strength of the resulting extruded material may be reduced. Furthermore, if the temperature of the extruded material after quenching exceeds 150° C., the quench hardening will be insufficient and the strength of the resulting extruded material may be reduced.

If the above-described cooling rate exceeds 100° C./sec., no commensurate effect can be obtained. On the other hand, if the cooling rate is lower than 2° C./sec., the quench hardening will be insufficient and the strength of the resulting extruded material may be reduced.

It is noted that a forced or active cooling means may be utilized in the quenching of the extruded material. For example, fan air cooling, mist cooling, shower cooling or water cooling can be employed during the quenching step.

The quenched extruded material is then subjected to an aging (precipitation hardening) treatment that involves heating the extruded material at a temperature of 150° C. to 200° C. for 1 to 24 hours. If the temperature during the aging treatment is lower than 150° C., the effects obtained by the aging treatment will be insufficient and the strength of the resulting extruded material may be reduced. On the other hand, if the temperature during the aging treatment exceeds 200° C., over-aging results and the strength of the resulting extruded material may be reduced.

If the heating time during the aging treatment is less than 1 hour, under-aging results and the strength of the resulting extruded material may be reduced. On the other hand, if the heating time during the aging treatment exceeds 24 hours, over-aging results and the strength of the resulting extruded material may be reduced.

EXAMPLES Example 1

This is an Example for investigating the chemical components (elemental composition) of the above-described high-strength aluminum alloy extruded material. In this Example, alloys (Alloys Nos. A to M) comprising the elements in various amounts as indicated in Table 1 were used to produce samples (Samples Nos. 1 to 13) according to the manufacturing conditions indicated in Table 2, and then strength measurements, metallographic structure observations, surface quality evaluations and corrosion resistance evaluations were carried out on the respective samples. Hereinafter, the conditions for manufacturing the respective samples and the methods for measuring their strength, observing their metallographic structure, evaluating their surface quality and evaluating their corrosion resistance will be explained in further detail.

<Manufacturing Conditions for the Samples>

Ingots having a diameter of 90 mm and containing the elements indicated in Table 1 were cast using a continuous casting technique. Thereafter, the ingots were subjected to a homogenization treatment that involved holding them at a temperature of 480° C. for 10 hours. Then, the ingots were subjected to hot extrusion at an extruding rate of 10 m/min. in a state where the temperatures of the ingots were maintained at the temperatures indicated in Table 2, thereby producing extruded materials having a flat bar shape with a width of 35 mm and a thickness of 3 mm. Then, the extruded materials were subjected to a quenching treatment that involved cooling them to the temperatures indicated in Table 2 at a cooling rate of 10° C./sec. in a state where the temperatures of the extruded materials were maintained at the temperatures indicated in Table 2. The quenched extruded materials were then subjected to an aging treatment that involved heating them at 180° C. for 6 hours, thereby producing the samples (Samples Nos. 1 to 13).

<Strength Measuring Method>

Test pieces (tensile test pieces of metal materials, No. 5 test pieces) were collected from the samples by a method in accordance with JIS 22241 (1506892-1) to measure the proof stress. As a result, the test pieces exhibiting a proof stress of 350 MPa or more were judged to be acceptable.

<Method for Observing Metallographic Structure>

After the samples were cut such that the dimension in the width direction was halved, the measurement of the particle diameter of the crystallized product in the cut surface and the calculation of the area ratio of the fibrous structure were carried out by the following methods.

In the measurement of the particle diameter of the crystallized products, the above-described cut surface was first polished to obtain a smooth surface. Five places on the smooth surface were randomly selected, and microscopic images of these five places were obtained at 500-times magnification using an optical microscope. Thereafter, image analysis was performed on the microscopic images, thereby obtaining a maximum value among the particle diameters of the crystallized products calculated using the above-described ellipse approximation method. The samples in which the thus-obtained maximum particle diameter of the crystallized products was 5 μm or less were judged to be acceptable.

In the calculation of the area ratio of the fibrous structure, the cut surface was subjected to electrolytic polishing and etching by the above-described method, and then a microscopic image of the above cut surface was obtained using an optical microscope so as to bring the entire range in the thickness direction into view. Thereafter, image analysis was performed on the resulting microscopic image to calculate the area ratio of the fibrous structure relative to the entire metallographic structure. The samples in which the thus-obtained area ratio of the fibrous structure was 95% or more were judged to be favorable.

<Method for Evaluating Surface Quality>

The surfaces of the samples were visually observed to confirm the presence or absence of defects such as surface exfoliation or streaky scratchs formed in the extruding direction. The samples having no such defects were judged to be acceptable.

<Method for Evaluating Corrosion Resistance>

Salt spray testing was performed on the respective samples by a method in accordance with JIS 22371 to measure the maximum corrosion depth after a 1000-hour testing time. As a result, those samples exhibiting a maximum corrosion depth of 200 μm or less were judged to be acceptable.

The evaluation results for each of the samples are indicated in Table 3. The evaluation results for the samples which were not judged as being acceptable or favorable are underlined in Table 3.

As can be seen from Table 3, Samples Nos. 1 to 3 were judged as being acceptable in terms of all the evaluation criteria and exhibited excellent properties in strength, corrosion resistance, extrusion productivity and surface quality properties. FIG. 1 shows a microscopic image used in the calculation of the area ratio of the fibrous structure of Sample No. 1 as one typical example having excellent properties. As shown in FIG. 1, the samples having excellent properties exhibit a metallographic structure, in which a recrystallized structure is generated only very near the surface; the insides of these samples are mostly comprised of a fibrous structure oriented in parallel to the extrusion direction.

Sample No. 4, the Si content of which was too low, was judged as being unacceptable in terms of proof stress.

Sample No. 5, the Si content of which was too high, was judged as being unacceptable because surface exfoliation was observed after the extrusion.

Sample No. 6, the Mg content of which was too low, was judged as being unacceptable in terms of proof stress.

Sample No. 7, the Mg content of which was high, was judged as being unacceptable because surface exfoliation was observed after the extrusion.

Sample No. 8, the Cu content of which was too low, was judged as being unacceptable in terms of proof stress.

Sample No. 9, the Cu content of which was too high, was judged as being unacceptable because surface exfoliation was observed after the extrusion and the corrosion resistance was poor.

Sample No. 10, the Mn, Cr and Zr contents of which were too low, was judged as being unacceptable due to the reduced proof stress that resulted from the low area ratio of the fibrous structure. FIG. 2 shows a microscopic image used in the calculation of the area ratio of the fibrous structure of Sample No. 10 as a typical example of samples having a low area ratio of the fibrous structure. As shown in FIG. 2, the metallographic structure of this sample having a low area ratio of the fibrous structure had a thick recrystallized structure generated on the surface as compared with that shown in FIG. 1, and a layer (recrystallized structure) having no streaky pattern and different in color hue from the fibrous structure was clearly observed near the surface.

Sample No. 11, the Mn, Cr and Zr contents of which were too high, was judged as being unacceptable because the particle diameter of the crystallized product was excessively large and surface exfoliation was observed after the extrusion.

Sample No. 12, the Ti content of which was too low, was judged as being unacceptable due to the reduced proof stress that resulted from the low area ratio of the fibrous structure.

Sample No. 13, the Ti, V and Fe contents of which were too high, was judged as being unacceptable because the particle diameter of the crystallized product was excessively large and surface exfoliation was observed after the extrusion.

Example 2

This is an Example for investigating methods for manufacturing the above-described high-strength aluminum alloy extruded material. In this Example, alloy No. A indicated in Table 1 was used to produce samples (Samples Nos. 21 to 39) according to the manufacturing conditions that varied as indicated in Table 4, and then the strength measurements, metallographic structure observations, surface quality evaluations and corrosion resistance evaluations were carried out on the respective samples. In this respect, it is noted that the details of the conditions for manufacturing the respective samples and the methods for measuring their strength, observing their metallographic structure, evaluating their surface quality and evaluating their corrosion resistance are the same as described above in Example 1.

The evaluation results for the respective samples are indicated in Table 5. It is noted that the evaluation results for the samples that were not judged as being acceptable or favorable are underlined in Table 5.

As can be seen from Table 5, Samples Nos. 21 to 30 were judged as being acceptable in terms of all the evaluation criteria, and exhibited excellent properties in strength, corrosion resistance, extrusion productivity and surface quality.

Sample No. 31, prepared at a too low holding temperature during the homogenization treatment, was judged as being unacceptable because the proof stress was low and surface exfoliation was observed after the extrusion.

Sample No. 32, prepared at a too high holding temperature during the homogenization treatment, was judged as being unacceptable due to the reduced proof stress that resulted from the low area ratio of the fibrous structure.

Sample No. 33, prepared at a too short holding temperature during the homogenization treatment, was judged as being unacceptable because the proof stress was low and surface exfoliation was observed after the extrusion.

Sample No. 34, prepared at a too low ingot temperature before hot extrusion, was judged as being unacceptable in terms of proof stress.

Sample No. 35, prepared at a too high ingot temperature before hot extrusion, was judged as being unacceptable because surface exfoliation was observed after the extrusion.

Sample No. 36, prepared at a too low cooling rate during the quenching treatment, was judged as being unacceptable in terms of proof stress.

Sample No. 37, prepared at a too high extruded material temperature after completion of the quenching treatment, was judged as being unacceptable in terms of proof stress.

Samples Nos. 38 and 39, prepared at an aging treatment time and temperature that fall outside the above-specified ranges, were judged as being unacceptable in terms of proof stress.

TABLE 1 Alloy Si Mg Cu Mn Cr Zr Ti V Fe Zn Al No. (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) (%) A 1.00 0.80 0.35 0.30 0.05 0.15 0.020 0.005 0.20 0.01 bal B 0.70 1.20 0.15 0.10 0.01 0.05 0.005 0.005 0.06 0.15 bal C 1.30 0.45 0.39 0.40 0.06 0.20 0.140 0.008 0.30 0.01 bal D 0.65 0.80 0.35 0.30 0.05 0.15 0.020 0.005 0.20 0.01 bal E 1.34 0.80 0.35 0.30 0.05 0.15 0.020 0.005 0.20 0.01 bal F 1.00 0.42 0.35 0.30 0.05 0.15 0.020 0.005 0.20 0.01 bal G 1.00 1.30 0.35 0.30 0.05 0.15 0.020 0.005 0.20 0.01 bal H 1.00 0.80 0.12 0.30 0.05 0.15 0.020 0.005 0.20 0.01 bal I 1.00 0.80 0.45 0.30 0.05 0.15 0.020 0.005 0.20 0.01 bal J 1.00 0.80 0.35 0.07 0.00 0.03 0.020 0.005 0.20 0.01 bal K 1.00 0.80 0.35 0.45 0.10 0.24 0.020 0.005 0.20 0.01 bal L 1.00 0.80 0.35 0.30 0.05 0.15 0.003 0.005 0.20 0.01 bal M 1.00 0.80 0.35 0.30 0.05 0.15 0.170 0.015 0.36 0.01 bal

TABLE 2 Hot Extruding Homogenization Ingot Quenching Aging Treatment Temperature Temperature Temperature Treatment Retaining Retaining before before Cooling immediately Treatment Treatment Sample Alloy Temperature Time extruding quenching Rate after quenching Temperature Time No. No. (° C.) (Hour) (° C.) (° C.) (° C./sec.) (° C.) (° C.) (Hour) 1 A 480 10 480 481 10 140 180 6 2 B 480 10 520 523 10 25 180 6 3 C 480 10 520 524 10 25 180 6 4 D 480 10 520 523 10 140 180 6 5 E 480 10 520 526 10 140 180 6 6 F 480 10 520 523 10 140 180 6 7 G 480 10 520 523 10 140 180 6 8 H 480 10 520 524 10 140 180 6 9 I 480 10 520 523 10 140 180 6 10 J 480 10 520 524 10 140 180 6 11 K 480 10 520 524 10 140 180 6 12 L 480 10 520 524 10 140 180 6 13 M 480 10 520 523 10 140 180 6

TABLE 3 Strength Observation of Evaluation of Evaluation of Test Metallographic Structure Surface Quality Corrosion Resistance Proof Maximun Area Ratio of Result of Maximum Sample Alloy Stress Particle Diameter Fibrous Structure Visual Corrosion Depth No. No. (MPa) (μm) (%) Observation (μm) 1 A 350 2 98 nondefective  65 2 B 356 2 95 nondefective 160 3 C 360 5 99 nondefective 150 4 D 330 2 98 nondefective  55 5 E 360 2 98 exfoliated 160 6 F 326 2 98 nondefective  60 7 G 382 2 98 exfoliated  70 8 H 318 2 98 nondefective  60 9 I 360 2 98 exfoliated 230 10 J 290 2 78 nondefective 180 11 K 380 6 99 exfoliated 100 12 L 348 2 93 nondefective  80 13 M 385 7 98 exfoliated 150

TABLE 4 Hot Extruding Homogenization Ingot Quenching Aging Treatment Temperature Temperature Temperature Treatment Retaining Retaining before before Cooling immediately Treatment Treatment Sample Temperature Time extruding quenching Rate after quenching Temperature Time No. (° C.) (Hour) (° C.) (° C.) (° C./sec.) (° C.) (° C.) (Hour)) 21 455 10 520 524 10 140 180 6 22 495 10 520 524 10 140 180 6 23 480  2 520 523 10 140 180 6 24 480 30 520 524 10 140 180 6 25 480 10 480 481 10 140 180 6 26 480 10 540 541 10 140 180 6 27 480 10 520 523  2 140 180 6 28 480 10 520 523 100  140 180 6 29 480 10 520 524 10  30 150 24  30 480 10 520 524 10  25 200 1 31 440 10 520 524 10 140 180 6 32 530 10 520 523 10 140 180 6 33 480  1 520 523 10 140 180 6 34 480 10 460 463 10 140 180 6 35 480 10 550 552 10 140 180 6 36 480 10 520 524  1 140 180 6 37 480 10 520 524 10 200 180 6 38 480 10 520 524 10  30 130 30  39 480 10 520 523 10  25 220   0.5

TABLE 5 Observation of Metallographic Evaluation Structure Evaluation of Corrosion Strength Area of Surface Resistance Test Maximun Ratio of Quality Maximum Proof Particle Fibrous Result of Corrosion Sample Stress Diameter Structure Visual Depth No. (MPa) (μm) (%) Observation (μm) 21 351 2 98 nondefective 60 22 375 2 98 nondefective 120 23 372 2 98 nondefective 150 24 373 2 98 nondefective 80 25 350 2 98 nondefective 65 26 384 2 98 nondefective 120 27 351 2 98 nondefective 155 28 374 2 98 nondefective 50 29 380 2 98 nondefective 70 30 351 2 98 nondefective 75 31 346 2 99 exfoliated 70 32 330 2 70 nondefective 110 33 342 2 98 exfoliated 150 34 312 2 98 nondefective 60 35 389 2 98 exfoliated 110 36 290 2 98 nondefective 170 37 285 2 98 nondefective 90 38 290 2 98 nondefective 65 39 330 2 98 nondefective 85

Representative, non-limiting examples of the present invention were described above in detail with reference to the attached drawings. This detailed description is merely intended to teach a person of skill in the art further details for practicing preferred aspects of the present teachings and is not intended to limit the scope of the invention. Furthermore, each of the additional features and teachings disclosed above may be utilized separately or in conjunction with other features and teachings to provide improved aluminum alloys and methods for manufacturing and using the same.

Moreover, combinations of features and steps disclosed in the above detailed description may not be necessary to practice the invention in the broadest sense, and are instead taught merely to particularly describe representative examples of the invention. Furthermore, various features of the above-described representative examples, as well as the various independent and dependent claims below, may be combined in ways that are not specifically and explicitly enumerated in order to provide additional useful embodiments of the present teachings.

All features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter, independent of the compositions of the features in the embodiments and/or the claims. In addition, all value ranges or indications of groups of entities are intended to disclose every possible intermediate value or intermediate entity for the purpose of original written disclosure, as well as for the purpose of restricting the claimed subject matter. 

What is claimed is:
 1. A high-strength aluminum alloy extruded material comprising: Si: 0.70 to 1.3 mass %; Mg: 0.45 to 1.2 mass %; Cu: 0.15 to less than 0.40 mass %; Mn: 0.10 to 0.40 mass %; Cr: more than 0 to 0.06 mass %; Zr: 0.05 to 0.20 mass %; Ti: 0.005 to 0.15 mass %, Fe: 0.30 mass % or less; V: 0.01 mass % or less; and the balance being Al and unavoidable impurities, wherein crystallized products in the alloy have a particle diameter of 5 μm or less, and wherein an area ratio of a fibrous structure in a cross section parallel to an extruding direction during hot extrusion is 95% or more.
 2. A structural member for vehicle comprising the high-strength aluminum alloy extruded material according to claim
 1. 3. A method for manufacturing a high-strength aluminum alloy extruded material, comprising: producing an ingot which comprises: Si: 0.70 to 1.3 mass %; Mg: 0.45 to 1.2 mass %; Cu: 0.15 to less than 0.40 mass %; Mn: 0.10 to 0.40 mass %; Cr: more than 0 to 0.06 mass %; Zr: 0.05 to 0.20 mass %; Ti: 0.005 to 0.15 mass %, Fe: 0.30 mass % or less; V: 0.01 mass % or less; and the balance being Al and unavoidable impurities; subjecting the ingot to a homogenization treatment that includes holding the ingot at a temperature of not lower than 450° C. and lower than 500° C. for 2 to 30 hours; subjecting the homogenized ingot to hot extrusion in a state where the temperature of the ingot at the start of the hot extrusion is held at 480° C. to 540° C. so as to form an extruded material; quenching the extruded material to 150° C. or lower at a cooling rate of 2° C./sec. to 100° C./sec. while the temperature of the extruded material is held at 480° C. or higher; and thereafter, subjecting the extruded material to an aging treatment that includes heating the extruded material at a temperature of 150° C. to 200° C. for 1 to 24 hours. 